Piano bridge



July 21, 1931.

Filed July 10. 1929 Patented July 21, 1931 UNITED STATES PATENT OFFICE LLOYD LOAR, OF CHICAGO, ILLINOIS, ASSIGNOR TO GULBRANSEN COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS PIANO BRIDGE Application filed July 10, 1929.

This invention relates to pianos, and more particularly to the construction of a piano bridge and the disposition thereof, relative to the sounding board.

In pianos of present date construction, the strings bear upon the upper face of the bridge at the center portion thereof so as to exert downward pressure upon the bridge vertically. Each string passes between two pins arranged adjacent the front and the back of the bridge and inclined oppositely to the direction of pull or tension exerted on the pin by the string.

Beyond each pin the upper lateral portion of the bridge is notched out to provide clearance for the string. This means that there are two holes drilled, two notches cut, and two pins set in the bridge for each string of a piano of what may be considered as regular or present day construction. All of this work has to be done by hand and expert work is required in properly positioning the pins. There are from 225 to 230 strings in a regular piano, so that the notching of the bridge, the drilling of the pin holes and the proper positioning of the pins is a material item in the cost of the instrument. I have also found that much better results can be obtained in tone 3 quality and volume by so relating the strings and the bridge construction as to permit of a rocking movement of the bridge, due to the vibration of the strings, instead of the vertical movement only which occurs in present day bridge construction.

One of the main objects of my invention is to provide a bridge construction which is of simple and relatively inexpensive type and is highly eflicient in service. A further object is to so relate the bridge and the strings and associated parts as to facilitate transmission of the string vibration to the sounding board. Further objects and advantages of my invention will appear from the detailed description.

In the drawings:

Figure 1 is a fragmentary plan View of a string plate and sounding board and bridge, and associated parts, mounted in the casing of a grand piano;

Serial No. 377,191.

Figure 2 is a Vertical sectional view, on an enlarged scale, through the sounding board and the treble and base bridges;

Figure 3 is a fragmentary plan view, on an enlarged scale, of the treble bridge and associated parts;

Figure 4 is a fragmentary vertical sectional View through the treble bridge and sound board showing a modified form of bridge construction.

I have illustrated my invention as applied to a sounding board 1 of a grand piano which comprises a casing 2 in which is suitably mounted a frame 3 which is disposed above board I. This frame comprises a string plate e. to which the strings are secured by suitable pins in a known manner, a wrest plate 5 in which the tuning pins are mounted, to which the strings are suitably secured, and cross braces and ribs. This frame is of known construction and is generally referred to as the plate. A bridge is mounted upon sounding board 1. This bridge is of irregular curvature in the direction of its length and conforms, in its 5 general outline, to bridges of present day construction. The bridge comprises a strip 6 which is of approximately rectangular cross-section except that the front face (in thereof is inclined downwardly and forwardly to the sounding board 1.

The strip 6 is of wood and seats flatly upon the upper face of board 1, being secured thereto in a suitable manner, as by a means of screws 7 which pass through the sounding board and screw into the strip. The head of screw 7 is countersunk into a wooden button 8 which bears flat against the under-face of sounding board 1 which is clamped between the button and the strip. Strip 6 is provided, in its top face and adj acent the front edge thereof, with an arcuate groove 9 which extends longitudinally of the strip and receives a cylindrical bearing member 10, which may be in the form of a steel rod approximately oneeighth of an inch in diameter, which seats in the groove. The forward portion of this groove constitutes an abutment element which serves to hold the bearing member 10 against inovement forwardly of the bridge structure when such member is subjected to the pressure of the strings.

A pressure plate 11 is disposed above strip 6 and in rear of bearing member 10. This plate has its under-face of substantially flattened ii-shape, being inclined downwardly and inwardly from each side. The corners and the vertex of the under-face of.

-. plate 11 are rounded so as to avoid sharp corners or edges which might contact with the strings. The pressure plate 11 is suitably bored for reception of screws 12 which pass through the plate and screw into strip 6. These screws provide means for securing the pressure plate to the strip and for forcing it toward the same.

A bridge structure for the base strings, is provided in rear of the treble bridge structure above described. This base bridge structure comprises a strip 6?) suitably secures to a relatively wide strip 13 the for ward portion of which is secured to a narrower strip 1 1 which seats upon the upper face of sounding board 1. Strips 13 and 1 1 are secured together and to the sounding board by screws 7, each screw having its head countersunk into a wooden button 8. The bridge strip 6?) is provided in its upper face with a groove 9 in which seats a string bearing member 10. A bearing or pressure plate 11 is secured to strip (it by screws 12 and has its under face of substantially flattened V-shape, as at 11a.

The strings are arranged upon the string plate in overstrung relation, as is known in the art, and these strings, designated by the reference character 15, pass over the bearing members 10 so as to bear upon the top portions thereof, and beneath the pressure plates 11. Pressure plate 11 exerts downward pressure upon the strings 15 so that the pressure exerted by these strings upon the member 10 is converted, in large part, from vertical pressure to pressure in a diagonal diner an toward the front edge of the bridge sq It will also be noted that the strings 15, being under tension, exert a liftiq effect upon the pressure plate 11, which e'i'fcct is transmitted o the rearward portion of the bridge strip by means of the screws 12.

This has a tendency to rock the bridge strip downwardly and forwardly and the vibration of the string is imparted to the bridge 6 in such manner as to cause transverse rocking movement thereof. This movement is transmitted to the sounding board 1 which thus has imparted thereto vibrations of greater amplitude than is possible where the strings exert downward vertical pressure only upon the bridge as in pianos of present day construction above referred to. In the case of the base bridge the rocking movement of the strip (3?) is transmitted to the sounding board 1 through the strip 13 and strip 14, strip 13 exerting a leverage effect.

The bridge construction illustrated and above described can be readily produced at comparatively small cost since the groove 9 can be readily formed in a suitable machine and the pressure plate 11 can be shaped and bored by machinery. This bridge construction can be quickly assembled and applied and effects a material saving in time over bridges of present day construction in which the bridge has to be notrned, the pin. holes have to be bored, and the pins set all by hand, as above described.

The pressure plate 11 is preferably made in sections of a length to extend between the cross bracs or ribs of the string plate. This is not i :ntial but is preferable as facilitatii'ig removal. and replaeenient of the pressure plate as desired or as conditions may require. It is also to be noted that this plate provides means whereby the tone of the instrument can be altered, within limits, by adjusting the pressure plate 11 toward and away from the bridge thus varying the tension of the strings.

In Figure 4, I have illustrated a modified form of my invention which. I have found to be highly etiieient. In this form the bridge strip 16 is of rectangular cross-section and has a relatively thin strip 17 so cured to its front face. This strip 17 projects upwardly a. short distance above the top of strip 16 and provides an abutment for the forward portion of the string bearing member 10. It will be noted that, in this form, there is no groove in the upper face of bridge strip 16. The construction and operation of this form of bridge structure is similar, in other respects, to the form illustrated in Figure 2. It will be noted that in both forms the pressure exerted by the strings 15 upon the bearing member 1.0 is transmitted to the forward portion of the bridge strip, which is the most efficient por tion thereof for vibrating the sounding board 1.

lVhile my bridge construction is equally well adapted for use with sounding boards of different types, I preferably use this bridge with a sounding board so constructed that the grain thereof extends transversely of the bridge, this board being provided on its under-face with a plurality of tone bars so relatively disposed as to connect the grain of the board throughout substantially the whole area thereof. One of these tone bars is shown at 18 in Figure 2 of the drawings.

The particular construction of this soundv ing board is disclosed in detail in my copending application for piano, tiled Decen'iber 21, 1928, Serial No. 328.238.

lVha I claim is: I

1. In combination in a piano bridge construction, a bridge strip having an abutment element adjacent its front face, a string bearing member seating upon the upper face of the strip in rear of and in contact with said element, and means for exerting pressure on the strings in the direction of the strip and in rear of the bearing member.

2. In combination in a piano bridge construction, a bridge strip having an abutment element adjacent its front face, a string bearing member seating upon the upper face of the strip in rear of and in contact with said; element, a pressure plate above the strip and in rear of the string bearing member, and means for forcing the plate toward the strip.

3. In combination in a piano bridge construction, a bridge strip having an abutment element adjacent its front face, a string bearing member seating upon the upper face 1; of the strip in rear of and in contact with said element, a pressure plate above the strip and in rear of the string bearing memher, and means for securing the plate to the strip and for forcing said plate toward the 5 strip.

In witness whereof, I hereunto subscribe my name this 13th day of June 1929.

LLOYD LOAR. 

